But the battlefield success hardly impressed two leading US senators, who on Sunday questioned the Pentagon's handling of the situation in Iraq and said they no longer had confidence in Defence Secretary Donald Rumsfeld.
Abu Zubair, also known as Muhammad Salah Sultan, was shot and killed in the northern city of Mosul on Friday, when he got caught in an ambush set up by Iraqi security forces, the officials said, confirming a report by Mosul police.
No other details of the operation were provided. But officials pointed out Abu Zubair was wearing a bomb belt filled with metal pellets when he was killed.
Abu Zubair was wanted for his alleged role in organising a bombing attack on an Iraqi police station in Mosul last month, in which five policemen were killed, according to the defence officials.
"I don't have confidence [in Rumsfeld]"
US Republican senator
They noted that Abu Zubair's death followed the capture of three bombmakers and six foreign fighters by US and Iraqi security forces last week.
"Abu Zubair's death, as well as recent captures of terrorists in northern Iraq, is making a difference in coalition and Iraqi security forces' efforts to disrupt terrorists operating in this part of the country," Colonel Bill Buckner, a spokesman for the multinational force, told reporters.
He expressed confidence that bombings and other attacks "will not prevent Iraqi democracy".
However, Joseph Biden, the top Democrat on the US Senate Foreign Relations Committee, said that judging by the way things were unfolding in Iraq, democracy there "will not happen in my lifetime".
He argued the most the Bush administration could hope for under the circumstances was a government that would be able to secure public safety and not be a threat to its neighbours.
Criticism of the administration's Iraq policy grew louder this month as the US casualty toll increased, raising the possibility that August will become one of the deadliest months for Americans this year.
At least 44 US military personnel have been killed in Iraq since the first of the month, despite a steady drumbeat of official assurances of progress.
"I think Rumsfeld should get his notice on Monday morning," Biden said as he appeared on NBC's Meet the Press programme.
Top US Democrat Senator Joseph
Biden urged Rumsfeld to go
Republican Senator John McCain, a possible presidential candidate in 2008, echoed the view, adding, "I don't have confidence" in Rumsfeld.
McCain was particularly incensed by recent statements by General George Casey, the top US military commander in Iraq, and other Pentagon officials that substantial withdrawals from Iraq could begin as early as next year.
"Look, I've got an idea for our Pentagon planners," the Arizona senator opined testily on the Fox News Sunday show.
No broad support
"The day that I can land at the airport in Baghdad and ride in an unarmed car down the highway to the 'green zone' is the day that I'll start considering withdrawals from Iraq."
Biden accused the defence secretary of being personally responsible for the US failure to get broader support for the US-led operation in Iraq from Nato allies.
"As long as Rumsfeld's in charge of this operation, as opposed to the uniformed military, they virtually have no confidence in our ability to get the job done," the Delaware Democrat pointed out.